1. Field of the Invention
This invention relates to a high-speed Belleville type seal for a rotary cone rock bit.
More particularly, this invention relates to a high-speed metal-to-metal Belleville seal for a rotary cone rock bit; the dynamic metal sealing surfaces being pre-lapped prior to assembly.
2. Description of the Prior Art
There are prior art patents that describe composite seals that are fabricated of resilient material that encapsulates or is adjacent to a metal sealing ring. For example, U.S. Pat. Nos. 4,344,629 and 4,394,020 both of which are assigned to the same assignee as the present invention, describes and teaches a metal-to-metal seal, the metal sealing surfaces of which are not pre-lapped prior to assembly. Both of these patents feature a resilient seal that initially operates to provide a seal while the metal-to-metal dynamic sealing surfaces are being lapped-in during operation of the rotary cone rock bit in a borehole. The U.S. Pat. No. 4,344,629 teaches a non-lapped metal ring that is encapsulated within a resilient material. The resilient material serves to initially provide a seal while the metal surfaces progressively lap themselves in as each rotary cone rotates on its journal while the bit works in a borehole. The U.S. Pat. No. 4,394,020 teaches a metal ring that is bonded to resilient material with a separate O-ring confined within an annular slot formed in the metal ring of the seal. The O-ring, like the U.S. Pat. No. 4,344,629 serves to provide the initial seal while the dynamic metal sealing surfaces are being lapped-in during bit operation.
U.S. Pat. No. 4,666,001 describes an earth-boring bit with metal-to-metal seals. A rigid face seal assembly is positioned between the cutter and bearing shaft of the rotary bit. The seal assembly moves axially in response to and to compensate for dynamic pressure changes in the lubricant adjacent to the seal. The metal-to-metal seal is designed to translate axially within an enlarged seal cavity during operation of the bit in a borehole to react to sudden changes of pressure across the seal face.
The foregoing patent is similar to a typical "Caterpillar" type seal, examples of which are found in U.S. Pat. Nos. 3,180,648, 3,403,916, and 3,524,654 all of which are assigned to the Caterpillar Corporation and which teach improvements to their basic metal-to-metal seal.
U.S. Pat. No. 4,306,727 describes a dynamic seal for sealing between a rotary cutter and a drill bit journal in an underground formation drilling bit. The seal utilizes a static elastomeric seal ring abutting a metal seal ring having a dynamic seal face. A metal sealing ring is biased against the cone surface by an elastomer wedged between the intersection of the leg and the journal and an L-shaped metal dynamic ring adjacent the cone.
Another related patent assigned to the same assignee as the foregoing patent teaches a very similar sealing arrangement, except that there are two dynamic L-shaped sealing rings that are suspended between two diagonally positioned elastomers such that the two L-shaped rings float in a seal cavity formed between the cone and the journal.
Another prior art U.S. Pat. No. 4,722,404 describes a low friction seal assembly for use with a rotary drill bit having bit cutters manufactured by casting the rotary cutters. The seal assembly includes a seal element having a Belleville spring surrounded by an elastomeric material. The static side of the seal is positioned in a roughened groove in the cast cone such that the inner dynamic sealing side of the Belleville seal is positioned near the intersection of the journal and the leg backface. Typically, a Belleville seal has the static side of the seal at this intersection of the journal in the leg backface, the dynamic sealing surface being adjacent the rotary cone. One embodiment of this patent discloses a metal ring adjacent the dynamic side of the Belleville seal that runs against a surface nearest the intersection of the journal and the leg backface.
These patents, while they illustrate and teach metal-to-metal seals, do not elaborate on materials of the metal seals. The present invention teaches the use of a static metal sealing ring, the sealing surface of which comprise a relatively softer metallic material than an opposite dynamic sealing surface. The static or non-moving seal ring of softer material is lapped against the harder material on the dynamic oppositely facing sealing ring. The hard and soft materials of the seal rings are prelapped prior to assembly of the seal between a journal bearing and a rotary cone. The softer sealing surface is preferably smaller in surface area than the harder dynamic sealing surface to accommodate for cone wobble or eccentricities that may occur between the cone and the journal during operation of the rotary cone rock bit in a borehole.
The first mentioned prior art patents assigned to the same assignee as the present invention taught the use of metal-to-metal seals that were not pre-lapped prior to use, the basic seal relying on a resilient material to provide the initial seal during the lapping process. The present invention differs in that the metal rings of the seal are pre-lapped, the softer static seal ring material, being run or lapped against the harder dynamic surface of the dynamic sealing ring.
The pressure compensated metal-to-metal floating sal previously described emphasizes the pressure compensating aspect of the seal assembly confined within a seal cavity and does not specifically teach the materials used in formulating the metal-to-metal seal.
The '727 patent, while it describes a metal-to-metal seal, does not elaborate on the materials of the dynamic seal faces within a rotary cone rock bit. The same is true for the '622 patent wherein back-to-back dynamic sealing rings are positioned within a sealed cavity of a rotary cone rock bit. These two patents emphasize the elastomeric material biased between the leg backface and the metal sealing ring adjacent the cone or similar L-shaped ring backed against the first ring.
The '404 patent, while it describes a Belleville type seal, illustrates the Belleville seal in a reverse configuration than is typical of a Belleville seal in a rotary cone rock bit. This particular patent is disadvantaged in that, since the dynamic seal surface is opposite to a standard Belleville seal, the Belleville seal as shown will act as a natural pressure relieving valve. Unfortunately, the valving action will admit debris that exteriorly surrounds the seal cavity. Standard Belleville type seals in the typical, reverse orientation will valve in the opposite direction, hence, lubricant will be expelled past the dynamic sealing faces thus purging the seal face of any detritus, rather than admitting contaminants therein.